I received and set up my new modem with Optus a day ago. I logged in with the wifi login details to all my devices. Less than 24hrs later I cannot get wifi on any of them and when I try to log back in using the identical login details I was supplied with, the password is not recognised. I did not change the password or login details.
Have you tried switching the modem off for a couple of minutes and then back on again? Might just need a reset